It is known to radiate primary light of a predefined primary light wavelength (e.g. blue light) onto a wavelength-converting ceramic body, where the primary light is converted at least partly into light of longer wavelength (e.g. into yellow light) and is re-emitted. The ceramic body can consist of rare-earth-doped ceramic having a garnet structure and typically has a laminar shape. It is usually irradiated centrally with the primary light. If the primary light is laser light and if the ceramic body is spaced apart from the laser that generates the primary light, this is also referred to as an LARP (“Laser Activated Remote Phosphor”) arrangement, with a miniaturized configuration being referred to as a μLARP arrangement. In this case, the German word “Phosphor” should not be understood to mean the element phosphorus, which is the same word in German, but rather generally the phosphor of the ceramic body or conversion element.
Upon the irradiation of the ceramic body, a significant local temperature increase occurs at the irradiation surface and can lead to generation of thermally induced stresses in the ceramic body and possibly to damage to the wavelength-converting ceramic body as a result of cracking. The risk of cracking can increase over time as a result of the primary light being repeatedly switched on and off, since a thermally induced alternating load associated therewith can lead to increased stress formation in the ceramic body.
Cracks in the wavelength-converting ceramic body have been able to be identified hitherto by means of complex optical analysis of the light emanating from the ceramic body.
A conventional conversion body includes a main body composed of wavelength-converting phosphor, which has an irradiation surface provided for irradiation with primary light, and at least one electrically conductive conduction track fitted on the main body outside the irradiation surface. A conversion device includes at least one conversion body and an evaluation device connected to the at least one conduction track, wherein the evaluation device is configured to ascertain a crack in the main body on the basis of a change in an electrical property of at least one conduction track. The conduction track consists of Al or a tungsten wire.
A critical aspect in the case of conversion devices is the configuration of the conduction track with regard to its evaluation. Furthermore, the contacting of the conduction track within the conversion device and toward the outside is also a technological challenge. By way of example, there are problems in the case of metallization since the typical contact elements on the carrier body lie for example 70 to 100 μm below the conduction track situated on the conversion body.